Reed switch having reed surfaces be-
neath the seal plated with a thin
silver layer

ABSTRACT

1. A SWITCHING DEVICE INCLUDING A PAIR OF ELONGATED NICKEL-IRON CONTACTS DISPOSED WITH THEIR TIPS IN OVER-LAPING RELATIONSHIP AND A GLASS ENVELOPE HERMETICALLY ENCAPSULATING THE OVERLAPPING PORTIONS OF SAID REED CONTACTS AND JOINED TO EACH OF SAID REED CONTACTS BY A GLASS-TO-METAL SEAL CHARACTERIZED IN THAT THE SURFACE OF EACH REED CONTACT,   INCLUDING THAT PORTION LOCATED BENEATH A SEAL, IS COVERED BY A (THIN) LAYER OF SILVER (.) HAVING A THICKNESS IN THE RANGE OF 60 TO 175 MICROINCHES.

Oct. 29, 1974 E. 1'. RATLJ F ETAL Rs. 28,220

REED swx'rcn uvms REED swam as aanm'ru "run snu. 'msn WITH A Tam SILVERmm Original Filed Sept. 23. 1971 FIG.

United States Patent Office Rei'ssued Oct. 29, 1974 28,220 REED SWITCHHAVING REED SURFACES BE- NEATH THE SEAL PLATED WITH A THIN SILVER LAYEREarl Truman Ratliff, Pataskala, and Paul William Renaut,

Columbus, Ohio, assignors to Bell Telephone Laboratories, Incorporated,Munay Hill and Berkeley Heights, N

Original No. 3,689,722, dated Sept. 5, 1972, Ser. No. 182,957, Sept. 23,1971. Application for reissue Sept. 24, 1973, Ser. No. 399,843

Int. Cl. C03c 27/04; H01h 51/28 US. Cl. 335-154 7 Claims Matter enclosedin heavy brackets appears in the original patent but forms no part ofthis reissue specification; matter printed in italics indicates theadditions made by reissue.

ABSTRACT OF THE DISCLOSURE A sealed contact dry reed switch in whichnickel-iron reed contacts are held in a glass envelope by seals and inwhich the surfaces of the reed contacts, including those portions underthe seals, are covered with a thin layer of silver.

BACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to dry reed contacts which are typically sealed in a glassenvelope to form a miniature switch and pertains in particular to thecomposition of a layer of conducting material disposed on the surface ofthe reed contacts.

2. Description of the Prior Art Miniature switches for controlling highfrequency signals must exhibit low insertion loss when used in highfrequency circuit applications. Where the switches comprise reedcontacts encapsulated in a glass envelope, the seals between the reedcontacts and the glass must be strong and reliable. Heretofore, lowinsertion loss has been achieved by plating the reed contacts with anoble metal such as gold-silver alloy such as disclosed in the articlebeginning at page 203, in Volume 48 of the Bell Laboratories Record. Ithas been difficult, however, to obtain suitable seal strengths.

Accordingly, one object of this invention is to achieve strong andreliable seals in reed switches adapted for high frequency use.

SUMMARY OF THE INVENTION In a preferred embodiment of this invention, apair of nickel-iron reed contacts disposed in overlapping relationshipwith each other inside a glass envelope are each held in place by a sealso as to form a miniature switch and the surfaces of each reed contact,including that portion beneath the seal, is covered with a thin layer ofsilver to improve the strength of the seal and to provide low insertionloss characteristics when the switch is used in a circuit carrying highfrequency signals.

According to one feature of this invention, improved seal strength, aswell as low insertion loss, is achieved by plating the reed contactswith a layer of silver having a thickness in the range of 60 to 175microinches.

DESCRIPTION OF THE DRAWING FIG. 1 is a side elevation view, taken insection, of a sealed contact dry reed switch made in accordance withthis invention;

FIG. 2 is an end elevation, taken in section along the lines 2-2, of thesealed contact dry reed switch illustrated in FIG. 1; and

FIG. 3 is an end elevation, taken in section along the lines 3-3, of thesealed contact dry reed switch illustrated inFIG. 1.

DETAILED DESCRIPTION Referring to FIG. 1, a sealed contact dry reedswitch 10 is disclosed which includes an encapsulating envelope 11 and apair of overlapping reed contacts 12. The envelope 11 is typically madeof glass, while the reed contacts 12 are made of a nickel-ironcomposition such as 52 alloy. Each reed contact 12 is firmly joined tothe vessel 11 by a seal 13 which is formed by melting the material ofthe envelope 11 until it adheres to the surfaces of the reed contacts12.

As best understood from FIGS. 1 and 2, the entire surface of each reedcontact 12 is covered by a silver layer 14. As shown in FIG. 3, eachreed contact 12 is separated from its seal 13 by the silver layer 14.

As is well known, if the reed contacts 12 are coated by a silver layer14, low insertion loss will be achieved when the reed switch 10 is usedin a high frequency application, i.e., frequencies up to megahertz. Ascan be seen from the following table, however, seal strengthsdrastically increase if the thickness of the silver layer 14 is limitedto a range of 60 to 175 microinches. When deposition conditions can beregulated closely, better results will be obtained by limiting thesilver layer 14 to a thickness in the range of 100 to microinches. Bestresults, however, will be achieved by limiting the thickness to 120microinches.

SEAL STRENGTH Silver Layer Thickness (Microinches) Mean Tensile Strength(Pounds) 0 12.0 60 13.5 118 15.0 13.5 233 12.0

While mating or contacting surfaces covered with silver can be used tomake and break electrical circuits, other contact materials arepreferable. Consequently, as shown in FIGS. 1 and 2, the overlappingportions of the reed contacts 12 are electrochemically stripped orotherwise treated until the silver layer 14 is removed. With theunderlying nickel-iron alloy exposed, other contact materials such as asilver-gold alloy can be disposed thereon to serve as a contact surface.

In summary, a sealed contact dry reed switch has been disclosed which issuitable for use in high frequency circuit applications and whichexhibits high seal strengths. While only a single embodiment has beendisclosed, it is illustrative of the principles of this invention andothers skilled in the art will readily conceive of others which willfall within the scope of the invention.

What is claimed is:

1. A switching device including a pair of elongated nickel-iron contactsdisposed with their tips in over-lapping relationship and a glassenvelope hermetically encapsulating the overlapping portions of saidreed contacts and joined to each of said reed contacts by aglass-to-metal seal characterized in that the surface of each reedcontact, including that portion located beneath a seal, is covered by a[thin] layer of silver [.1 having a thickness in the range of 60 to 175microinches.

[2. A switching device in accordance with claim 1 wherein the thicknessof said layer of silver lies within the range of 60 to 175 microinches.]

3. A switching device in accordance with claim [2] I wherein acontacting portion located on one reed contact in registration with thecorresponding contact portion on the other reed contact is devoid of asilver layer.

4. A switching device in accordance with claim 1 wherein the thicknessof said layer of silver lies within the range of 100 to 150 microinches.

5. A switching device in accordance with claim 1 wherein the thicknessof said layer of silver is 120 microinches.

6. A reed switch comprising a pair of metallic reed contacts disposedwith their tips in overlapping relationship and a glass envelopehermetically encapsulating the overlapping portions of the contacts andjoined to each of the contacts by a glasst0-metal seal characterized inthat the contact surface located beneath each seal is coated with alayer of silver between 60 and 175 microinches thick.

7. A reed switch in accordance with claim 6 wherein the layer 0 silveris between 100 and 150 microinches thick.

8. A reed switch in accordance with claim 6 wherein the layer of silveris 120 microinches thick.

References Cited The following references, cited by the Examiner, are ofrecord in the patented file of this patent or the original patent.

4 UNITED STATES PATENTS 3,497,655 2/1970 Rifl 200166 C 3,029,559 4/1962Treptow 6543 X 2,771,969 11/1956 Brownlow 6543 X 2,651,144 9/1953 Foleyet a1. 65-43 X 2,480,453 8/1949 Dorgelo et a] 6543 X 2,450,130 9/1948Gordon et al 65-43 X 3,495,061 2/1970 Coffin et al 200166 C 3,251,1215/1966 Prival 200166 C X 3,249,728 5/1966 Sasamoto et al. 200166 C2,469,878 5/1949 Hannon et a1 200166 C FOREIGN PATENTS 1,078,251 3/1960Germany 335-154 OTHER REFERENCES Isert, Problems of Selecting andOptimally Treating Material for Producing Sealed Reed Contacts, Thesis,received in German Patent Ofilce, Aug. 29, 1968, pp. 44 45.

ROBERT K. SCHAEFER, Primary Examiner W. J. SMITH, Assistant Examiner

1. A SWITCHING DEVICE INCLUDING A PAIR OF ELONGATED NICKEL-IRON CONTACTSDISPOSED WITH THEIR TIPS IN OVER-LAPING RELATIONSHIP AND A GLASSENVELOPE HERMETICALLY ENCAPSULATING THE OVERLAPPING PORTIONS OF SAIDREED CONTACTS AND JOINED TO EACH OF SAID REED CONTACTS BY AGLASS-TO-METAL SEAL CHARACTERIZED IN THAT THE SURFACE OF EACH REEDCONTACT,